Field of the Invention
The invention relates to a circuit configuration for supplying an electric motor which has a stator (arranged in a fixed position) and a moving rotor which is mounted, in particular, such that it can rotate. The stator has a large number of electromagnets which are arranged annularly and the rotor has a large number of permanent magnets which are associated with the electromagnets on the stator and are arranged, in particular in the form of a ring. A rectifier circuit provides for the conversion of the a.c. voltage which is drawn from the supply network to a d.c. voltage, and a converter circuit provides for the conversion of the d.c. voltage to a controllable frequency a.c. voltage which is used for supplying the electric motor.
Prior art circuit configurations of this type comprise a rectifier circuit which is used to convert the a.c. voltage, in particular a three-phase a.c. voltage, which is drawn from the supply network to a d.c. voltage. The rectifier circuit is connected to a converter circuit which produces an a.c. voltage which is used as the supply voltage for the electric motor. The drive control for the electric motor is provided by controlling the frequency and amplitude of the a.c. voltage which is produced from the d.c. voltage. A circuit part which contains capacitors and which provides the required smoothing for the d.c. voltage is located between the rectifier circuit and the converter circuit.
The a.c. voltage which is produced from the d.c. voltage supplies the electromagnets on the stator to attract or repel the permanent magnets which are arranged on the rotor, thus moving the rotor.
If the electromagnets are arranged in groups which in each case act on their own, the operation of the electric motor is ensured even if individual electromagnets fail.
A circuit configuration such as this does not always comply with the requirements placed on it since, if the supply voltage fails, the power which is required to operate the drive motor fails immediately, so that the system comes to rest abruptly. However, since it is absolutely essential in a large number of systems for the movement to cease smoothlyxe2x80x94such systems including, for example, cable car systems and similar driven systemsxe2x80x94there is a requirement to provide a flywheel mass, whose kinetic energy allows the system to come to rest slowly.
It is accordingly an object of the invention to provide a circuit configuration for supplying an electric motor which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which supplies a drive motor and ensures that the movement stops smoothly even when no flywheel mass is provided.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for supplying an electric motor, comprising:
a rectifier circuit for receiving an a.c. voltage from a supply network and for converting the a.c. voltage to a d.c. voltage;
a converter circuit for converting the d.c. voltage to a controllable-frequency a.c. voltage for driving the electric motor; and
an energy storage circuit containing an accumulator connected between the rectifier circuit and the converter circuit.
In accordance with an added feature of the invention, the accumulator comprises at least one rechargeable battery or a bank of series-connected rechargeable batteries. In a preferred embodiment, the energy storage circuit includes one or more capacitors connected in parallel with the accumulator.
In accordance with another feature of the invention, the stator of the electric motor has a plurality of groups of electromagnets, and the converter circuit is one of a plurality of converter circuits each associated with a respective one of the plurality of electromagnets, and the energy storage circuit is one of a plurality of energy storage circuits each associated with a respective one of the plurality of electromagnets.
With the above and other objects in view there is also provided, in accordance with the invention, an electric motor drive assembly, comprising:
an electric motor having a stator with a plurality of annularly disposed electromagnets and a rotor with a plurality of annularly disposed permanent magnets associated with the electromagnets of the stator;
a rectifier circuit for receiving an a.c. voltage from a supply network and for converting the a.c. voltage to a d.c. voltage;
a converter circuit connected to the electric motor, the converter circuit being configured to convert the d.c. voltage to a controllable-frequency a.c. voltage for driving the electric motor; and
an energy storage circuit containing an accumulator connected between the rectifier circuit and the converter circuit.
In other words, the objects of the invention are achieved by providing at least one energy storage circuit, which contains a rechargeable electrical device, between the rectifier circuit and the converter circuit.
The energy storage circuit preferably has at least one group of series-connected rechargeable batteries. In this case, the energy storage circuit may also, in a manner known per se, contain at least one capacitor, which is connected in parallel with the at least one rechargeable battery. According to a further preferred embodiment, the stator of the electric motor has a number of groups of electromagnets, which each have their own associated energy storage circuits and converter circuits.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for supplying an electric motor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.